Cancer fatalities in the United States alone number in the hundreds of thousands each year. Despite advances in the treatment of certain forms of cancer through surgery, radiotherapy, and chemotherapy, many types of cancer are essentially incurable. Even when an effective treatment is available for a particular cancer, the side effects of such treatment can be severe and result in a significant decrease in quality of life.
Most conventional chemotherapy agents have toxicity and limited efficacy, particularly for patients with advanced solid tumors. Chemotherapeutic agents cause damage to non-cancerous as well as cancerous cells. The therapeutic index of such compounds (a measure of the ability of the therapy to discriminate between cancerous and normal cells) can be quite low. Frequently, a dose of a chemotherapy drug that is effective to kill cancer cells will also kill normal cells, especially those normal cells (such as epithelial cells) which undergo frequent cell division. When normal cells are affected by the therapy, side effects such as hair loss, suppression of hematopoesis, and nausea can occur. Depending on the general health of a patient, such side effects can preclude the administration of chemotherapy, or, at least, be extremely unpleasant and uncomfortable for the patient and severely decrease quality of the remaining life of cancer patients. Even for cancer patients who respond to chemotherapy with tumor regression, such tumor response often is not accompanied by prolongation of progression-free survival (PFS) or prolongation of overall survival (OS). As a matter of fact, cancer often quickly progress and form more metastasis after initial response to chemotherapy. Such recurrent cancers become highly resistant or refractory to chemotherapeutics. Such rapid recurrence and refractoriness, after chemotherapy, are considered to be caused by cancer stem cells.
Recent studies have uncovered the presence of cancer stem cells (CSC, also called tumor initiating cells or cancer stem-like cells) which have self-renewal capability and are considered to be fundamentally responsible for malignant growth, relapse and metastasis. Importantly, CSCs are inherently resistant to conventional therapies. Therefore, a targeted agent with activity against cancer stem cells holds a great promise for cancer patients (J Clin Oncol. 2008 Jun. 10; 26(17)). Therefore, conventional chemotherapies can kill the bulk of cancer cells, but leave behind cancer stem cells. Cancer stem cells can grow faster after reduction of non-stem regular cancer cells by chemotherapy, which is consider the mechanism for the quick relapse after chemotherapies.
STAT3 is an oncogene which is activated in response to cytokines and/or growth factors to promote proliferation, survival, and other biological processes. STAT3 is activated by phosphorylation of a critical tyrosine residue mediated by growth factor receptor tyrosine kinases, Janus kinases, or the Src family kinases. Upon tyrosine phosphorylation, STAT3 forms homo-dimers and translocates to the nucleus, binds to specific DNA-response elements in target gene promoters, and induces gene expression. STAT3 activates genes involved in tumorigenesis, invasion, and metastasis, including Bcl-xl, Akt, c-Myc, cyclin D1, VEGF, and survivin. STAT3 is aberrantly active in a wide variety of human cancers, including all the major carcinomas as well as some hematologic tumors. Persistently active STAT3 occurs in more than half of breast and lung cancers, colorectal cancers, ovarian cancers, hepatocellular carcinomas, and multiple myelomas, etc; and more than 95% of head/neck cancers. STAT3 is considered to be one of the major mechanism for drug resistance of cancer cells. However, STAT3 has proven a difficult target for discovering pharmaceutical inhibitor. So far, no direct inhibitor of STAT3 with clinically-relevant potency has been identified after decades of efforts in the industry.
Accordingly, there exists a need for discovering compounds and pharmaceutical compositions for selectively targeting cancer cells, for targeting cancer stem cells, and for inhibiting STAT3, and methods of preparing these compounds and pharmaceutical compositions for clinical applications.
The references cited herein are not admitted to be prior art to the claimed invention.